Discharge lamp

Abstract: The object of the invention is to provide a discharge lamp, where use is made of resonance lines, which are emitted by ions in an excitation state and which has a high short wave ultraviolet ray output. According to the invention this object is achieved in the case of a lamp, which is provided with a pair of electrodes (4,5) having a reciprocal spacing of equal to or smaller than 12 mm. The lamp is of the electrode-stable type. As the major emission material cadmium is encapsulated in a quantity permitting a partial pressure P in operation of 3 x 10³ Pa to 1.3 x 10⁵ Pa. The lighting operation is performed in a state in which the lamp current J L fulfils the following condition (a): 0.7 < J L /P 1/4 < 15.0 According to the invention the object is also achieved in that as the major emission material zinc is encapsulated in a quantity permitting a partial pressure P in operation of 1 x 10³ Pa to 0.3 x 10⁵ Pa and the lighting operation is performed in a state in which the lamp current J L fulfils the following condition (b): 0.7 < J L /P 1/4 < 16.9

Description: The invention relates to a discharge lamp, in which an emission or irradiation is obtained through resonance lines, which are emitted from ions in an excitation state. Moreover, the invention relates to a lamp operation method for operating such discharge lamps. Conventionally in the case of a known discharge lamp an emission through spectral lines is used, which are emitted within an arc formed between electrodes at transitions of atoms or ions from one excitation state to another excitation state or ground state. Resonance lines, which are among the emission spectral lines, which are emitted at transitions of atoms or ions from one excitation state into a ground state, due to their high transition probability, generally have a high radiation factor, potentially. Lamps, whose irradiated resonance lines are short-wave ultraviolet rays, therefore have a very high industrial value. Lamps with a high output of short-wave ultraviolet rays are e.g. necessary in photochemical industries, in the manufacture of semiconductor devices, etc. There are adequate possibilities for covering such needs. However, in the presently used discharge lamps it is considered disadvantageous that there is unavoidably a so-called self absorption phenomenon. This means that optically-thick spectral lines such as resonance lines, which are emitted within the arc from the atoms or ions in the excitation state, are absorbed to a high degree by similar atoms or ions. These atoms or ions simultaneously coexist in a ground state. The consequence of this the radiation light to be obtained through the resonance lines is not radiated to the outside with a high radiation intensity from the lamp and in practice the latter is unusable. For example, in the case of a mercury arc lamp of the short arc type, resonance lines with wavelength of 185 nm and 254 nm emitted by Hg in an excitation state within a high temperature arc are absorbed by Hg, which is present in a part having a low temperature in a periphery of the arc and is in a ground state. Therefore the resonance lines are only radiated to the outside from the lamp to a very small extent. In the case of discharge lamps an emitted light intensity can normally be increased by raising a partial pressure of a major emission material and by increasing the temperature of the emission atoms or ions during operation. However, resonance lines can only be emitted by reducing the self-absorption phenomenon. For example, resonance lines with the wavelength 254 nm and which are emitted by Hg, only have an adequate intensity for industrial uses in the case of a mercury arc lamp with an extremely low pressure of approximately 0.1 Pa. Thus, for the reason indicated hereinbefore, there is neither a usable medium pressure lamp, nor a usable high pressure lamp with a high output of short wave ultraviolet rays. EP-A-0 599 229, published on June 1, 1994, discloses a cadmium/rare gas discharge lamp of the short arc type wherein cadmium is encapsulated with a pressure of 14 to 200 kPa in a stationary lighting operation. The lamp is operated such that the ratio of the discharge current in amperes to the cadmium pressure in kiloPascals during the stationary lighting operation lies in the range of from 0.13 to 15. GB-A-600495 discloses a short arc discharge lamp wherein a high luminous efficiency is achieved by means of a high pressure of Zn. The inclusion of this element in this basically Hg discharge lamp, which is particularly aimed at general illumination purposes, is to provide for a red colour correction of the light produced thereby. The invention has been made on the basis of the above-described facts. The object of the invention is to provide a discharge lamp, in which it is possible to use resonance lines, which are emitted from zinc ions in an excitation state and which have a high short wave ultraviolet ray output. A further object is to provide a method for operating a discharge lamp using zinc as the major emission material. According to the invention this object is achieved in that a discharge lamp is provided with a pair of electrodes having a reciprocal spacing of equal to or smaller than 12 mm and whose arc is stabilized by means of the electrodes, wherein zinc as the major emission material is encapsulated in a quantity permitting a partial pressure in operation of 10 3 Pa to 3 x 10 4 Pa and wherein the lamp operation can be performed such that 0.7 < J L /P 1/4 < 16.9 wherein J L represents the lamp current in A and P represents the partial pressure of the zinc in Pa. In addition, the object is achieved according to the invention with a method for operating a discharge lamp having a pair of electrodes reciprocally spaced by 12 mm or less, whose arc is stabilized by the electrodes and containing zinc as the major emission material in a quantity permitting a partial pressure in operation between 10 3 and 3 x 10 4 Pa according to which the lamp current is such that the condition 0.7 < J L /P 1/4 < 16.9, wherein P represents the partial pressure of the zinc in Pa and J L represents the lamp current in A, is fulfilled. As a result of the above-described arrangement, in which an adequately high temperature is achieved within the arc formed between the electrodes and which is kept constant, a relatively large amount of zinc as the major emission material is ionized within the above-described arc, so that a state is obtained in which there is a high density of zinc ions Zn + . However, due to the low temperature of the above-described periphery of the arc, in the latter zinc as the main emission material is scarcely ionized, so that a state is obtained in which there is a low density of zinc ions Zn + . As a consequence of this resonance lines with a wavelength of 202.6 nm, which are emitted by Zn + within the arc, are radiated to the outside from the lamp with a high intensity. An embodiment of the discharge lamp according to the invention or for use in the lamp operation method of the invention described in greater detail hereinafter relative to the drawing, wherein fig. 1 shows a diagrammatic cross-sectional view of an embodiment of the discharge lamp according to the invention or for use in the lamp operation method of the invention. Fig. 1 diagrammatically shows in cross-section an embodiment of a discharge lamp according to the invention or for use in the lamp operation method of the invention. In Fig.1, a glass arc tube is designated 1. The arc tube is centrally provided with an approximately spherical enlargement 2, which has a separated inner space. On both ends of the arc tube 1 is located a sealed portion 3. Within the inner space are positioned in facing manner a cathode 4 and an anode 5. The base of the cathode 4 and the base of the anode 5 are in each case connected to a metal foil 6 hermetically enclosed within the sealed portion 3. Each of the metal foils 6 is connected to an outer base pin 7. This discharge tube has an arrangement as a lamp of the electrode-stable type, i.e. a lamp, whose arc is stabilized by means of the electrodes. There is a spacing L between the cathode 4 and the anode 5 equal to or smaller than 12 mm and a L/D, i.e. a ratio between the spacing between the electrodes L and a maximum internal diameter D perpendicular to the electrode direction of the envelope 2, which is e.g. smaller than 1, and an arc state is stabilized by the electrodes. Within the inner space subdivided by the envelope 2 is encapsulated zinc as the major emission material. The zinc is encapsulated in a quantity permitting a partial pressure P of the major emission material in operation of 10 3 Pa to 3 x 10 4 Pa and lamp operation is performed with a lamp current J L , which fulfils the following condition (b): Condition (b) 0.7 < J L /P 1/4 < 16.9 The zinc is encapsulated during lamp manufacture as zinc metal or zinc halide or an admixture thereof. If necessary, within the inner space can be encapsulated as a buffer gas rare gas, such as argon, krypton or the like, or mercury or the like. As the lamp, in the case of the above-described arrangement, is operated at an extremely high lamp current J L , an adequately high temperature is reached within the arc formed and kept constant between the cathode 4 and the anode 5. As a consequence of this a relatively large amount of zinc as the major emission material is ionized within the above-described arc, which leads to a state in which there is a very high density of zinc ions Zn + . However, in the periphery of the arc, zinc as the major emission material, as a result of the large temperature difference compared with that in the arc, through being stabilized by the cathode 4 and the anode 5, scarcely undergoes ionization and this leads to a state in which there is a low Zn + density. Therefore the self-absorption phenomenon only rarely occurs and the lamp operation is performed in a state in which the resonance lines, which are emitted by the Zn + within the arc, are emitted to the outside from the lamp with a high intensity, as is made apparent from the subsequent test examples. However, if the spacing L between the cathode 4 and the anode 5 is greater than 12 mm, a larger arc shape occurs. It is not therefore desirable to use that kind of lamp together with a focussing mirror, because then there is a reduction of the focussing efficiency. In the case that the partial pressure P rises in operation above 3 x 10 4 Pa, there is a drop of the emission line intensity to be obtained through zinc ions, because zinc ions absorb their resonance line with a wavelength of 213.86 nm and this takes place in a larger quantity. If the lamp current is low and the value of the ratio J L /P 1/4 is equal to or smaller than 0.7, the zinc is not adequately ionized within the arc, because it is difficult to adequately increase the temperature within the arc. The intensity of the resonance lines radiated to the outside decreases, because the density of the Zn + is low and at the same time the self-absorption phenomenon occurs more frequently. In the case that the lamp current J L is high and the value of the ratio J L /P 1/4 is equal to or greater than 16.9, the major temperature of the periphery of the arc also increases. Therefore the zinc of the periphery of the arc is ionized and the resonance lines emitted within the arc by Zn + are relatively more frequently absorbed by the Zn + in a ground state in the arc periphery. As described hereinbefore, as a result of the measure of fulfilling the above condition, a high intensity and a high efficiency are obtained, so that there is a transient power of the resonance lines emitted by Zn + . When performing the invention it is desirable for obtaining a state in which the condition 0.7 < J L /P 1/4 < 16.9 is fulfilled, to operate the discharge lamp according to the invention so that it is inserted within an outer jacket tube and that air layers are formed around the arc tube 1, so that there is an advantageous, high temperature within the arc. As a result of this measure with a temperature of a wall of the arc tube 1 of e.g. approximately 1000 to 1200 K, a stable state can be easily obtained, in which the arc centre temperature is approximately 9000 to 10,000 K. For the stable maintenance of the arc state, it is also desirable to perform the lighting operation using a vertical lighting operation system, i.e. in a state in which the electrodes face one another at the top and bottom. Hereinafter a specific test example of the invention is described. However, the invention is not restricted to the lamp described therein. A discharge lamp was manufactured in such a way that within an arc tube having a spacing L between the electrodes of 5 mm and an inner space with a volume of 22.1 cm 3 , 7 mg of zinc element and argon gas were encapsulated (with a pressure of 0.3 MPa (3 atm) on encapsulation). This discharge lamp was operated within an outer jacket tube using a vertical lighting operation system and under a condition whereby the lamp current J L was 41 A. The partial pressure P of the zinc in operation was 6 x 10 4 Pa, the ratio J L /P 1/4 was 2.6 and the electric input power Q was 575 W. With respect to the light radiated by the discharge lamp a spectral intensity distribution in a wavelength range 200 to 250 nm was measured, on the basis of the measuring diagram an integrated value  of the light intensity in a wavelength range 201 to 208 nm was determined and a ratio between said integrated value  and the electric input power Q (/Q) x 100 was calculated. The integrated value  was at 28.5 and the ratio (/Q) x 100 at 5.0. According to the invention resonance lines emitted by zinc ions within an arc have a high intensity due to a high density of the above-described ions within the arc and at the same time, due to a low density of the zinc ions in the periphery of the arc are emitted to the outside by the lamp with a high intensity. Thus, the invention provides a discharge lamp having zinc encapsulated as the major emission material having a high short wave ultraviolet ray output and having high radiance. Moreover, the invention provides a method of effectively operating discharge lamps wherein zinc is encapsulated as the major emission material.

Claims: A method for operating a discharge lamp having a pair of electrodes reciprocally spaced by 12 mm or less, whose arc is stabilized by the electrodes and containing zinc as the major emission material in a quantity permitting a partial pressure in operation between 10 3 and 3 x 10 4 Pa according to which the lamp current is such that the condition 0.7 < J L /P 1/4 < 16.9, wherein P represents the partial pressure of the zinc in Pa and J L represents the lamp current in A, is fulfilled. A discharge lamp provided with a pair of electrodes having a reciprocal spacing of equal to or smaller than 12 mm and whose arc is stabilized by means of the electrodes, wherein zinc as the major emission material is encapsulated in a quantity permitting a partial pressure in operation of 10 3 Pa to 3 x 10 4 Pa and wherein the lamp operation can be performed such that 0.7 < J L /P 1/4 < 16.9, wherein J L represents the lamp current in A and P represents the partial pressure of the zinc in Pa.

Inventors: HIRAMOTO TATSUMI, IGARASHI TATSUSHI, MATSUNO HIROMITSU, YAMAGUCHI AKIYASU, YASUDA YUKIO, HIRAMOTO, TATSUMI, IGARASHI, TATSUSHI, MATSUNO, HIROMITSU, YAMAGUCHI, AKIYASU, YASUDA, YUKIO
Applicants: USHIO ELECTRIC INC, USHIODENKI KABUSHIKI KAISHA
Application year: 1994
Main classification: H01J61
IPC codes: G03F7, H01J61